1. Field of the Invention
This invention relates to an apparatus for manufacturing a spring unit used for mattresses and the like.
2. Description of the Related Art
Japanese Utility Model Publication No. 35,573/78 discloses an apparatus for manufacturing a spring unit, in which a plurality of coil springs ar formed by bending a resilient wire. These coil springs form a spring band having a predetermined thickness, such that coil springs are arranged side by side in a row and their side limbs are adjacent to one another. The spring units further comprise helical wires which interconnect the side limbs of the spring band. These helical wires are wound around the side limbs by moving the helical wires in the axial direction thereof while the helical wires are rotated in a manner of a screw in a direction transverse to the spring band. After the helical wires are wound to the spring band, the ends of the helical wires are cut off and then bent by a tool, in the end treatment.
Where the spring bands are used for mattresses, the width of the spring bands varies, depending on the sizes of the mattress, that is, whether the mattress is used for a double size, semi-double size or single size bed. Therefore, it is necessary to vary the feeding length of the helical wires in accordance with the width of the spring bands. However, in the prior apparatuses for manufacturing spring units, the feeding length of the helical wire is not automatically controlled in accordance with the width of the spring bands.
Further, the opposite ends of the helical wires wound around the spring bands are cut off and bent by the tool, in the end treatment. The tool is, however, provided in a fixed position in relation to the width direction of the spring bands. Therefore, when the width of the spring bands is changed from that for the double size to that for the semi-double or single size, the position of the tool is deviated from the lateral borders of the spring bands in the width direction thereof, so that the ends of the helical wires are no longer treated by the tool.
Further, the prior art apparatus for making the spring unit, as disclosed in the publication, is not provided with any means for forming straight wires into helical form and automatically feeding these helical wires to the side limbs of the spring bands. Therefore, it is necessary to perform, as independent steps, a step of forming helical wires and a step of combining these helical wires with the spring bands, thus causing the productivity of workers making the spring units to be reduced.